Combined detector-automatic volume control circuits



July 21, 1936- I D. G. BURNSI,DE

COMBINED DETECTOR AUTOMATIC VOLUME CONTROL CIRCUITS Filed NOV. 25, 1952DON G. BURNSIDE lfg/wv ATTORN EY- Patented July 21, 1936 COMBINEDDETECTOR-AUTOMATIC VOLUME CONTROL CIRCUITS Don 'G. Burnside,Philadelphia, Pa., assignor to Radio Corporation of America, acorporation of Delaware Application November 25, 1932, Serial No.644,149

' 11 Claims. (01. 250-20) My present invention relates to improvementsin combined detector-automatic volume control circuits, and moreparticularly to circuits of this typev .whichutilize tubes of theduplex-diode triode type. V

. There is disclosed by T. M. Shrader in application Serial. No.622,140, filed July 12, 1932, a multiple duty electron discharge tubeknown as a duplex diode-triode, and designated numerically as of the 55type. In the said application there have also been disclosed variouscircuit arrangements for utilizing such a tube as a combineddetector-automatic volume control tube; the said circuit arrangementsare claimed in Shrader divisional application Serial No. 686,718,

filed August 25, 1933. Briefly, it may be stated that such a tube iscapable of simultaneous use as a detector or demodulator, an amplifier,and also'urce of automatic volume control potential. In'generaLsuch atube comprises one, or more.

. diodev sections and a triodesection, all disposed within a single tubeenvelope.

Summarizing the disclosures of the aforementionedapplicationait can bestated that there is provided a single electron discharge device whichis mechanically. a unitary device, but, functionally, is an amplifyingtriode, and 2; rectifier having two anodes which are electricallyindependent of each other and of the amplifier. Such a device has manyapplications, and has very great flexibility for use with many differentkinds, of. circuits because of the electrical independence or the diodesand the amplifier. The electrodes of the device 'are enclosed in asingle envelope, and are combined in a single mount having a commoncathode, with the grid and plate of the amplifier surrounding thecathode near one end, and the rectifier anodes mounted near the otherend on independent leads.

' One of the main objects of the present invention is to provide acircuit including half wave diode rectification for detection andautomatic volume control, the rectification further furnishing theself-bias of the grid of the triode section of 'atube of the duplexdiode-triode type.

And still another object of the present invention is to provide acircuit and tube combination, the tube being of the duplex diode-triodetype, embodying delayed automatic volume control in order that theordinary noises present in the receiver may not be reproduced in theabsence of the carrier.

And still other objects of the invention are'to improve generally thesimplicity and efiiciency of receivers employing combineddetector-auto-' matic volume control-audio frequency amplifier stages,and to particularly provide a receiver of this kind which is not onlyreliable in operation, but economically manufactured and assembled.

The novel features which I believe to. be characteristic of my inventionare set forth in particularity in the appended claims, the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin 20 connection with the drawing in which I have indicateddiagrammatically several circuit organizations whereby my invention maybe carried into effect. 1 1

In the drawing,

Fig. 1 diagrammatically showsa superheterodyne receiver employing amultiple duty tube embodying one form of the'present invention;

Fig. 2 shows a portion of the receiver in Fig. 1 embodying a modifiedform of the invention; and,

Fig. 3 shows a further modification of the invention.

Referring now to the accompanying drawing wherein like referencecharacters in the different figures designate similar circuit elements,Fig. 1 diagrammatically showsa'receiver of the superheterodyne type,wherein the second detector stage includes a circuit and tubecombination employing the present invention; Thus, in Fig. 1, there isshown preceding the multiple duty tube I the conventionalsuperheterodyne receiver stages. As is well known in the art, such areceiver usually embodies a radio frequency amplifier which is tunable,a local oscillator, a first detector and an intermediate frequencyamplifier of one, or more, stages. The output of the intermediatefrequency amplifier is. impressed upon the, second detector, and theaudio frequency output of the second detector is supplied to an audiofrequency amplifier, and finally a reproducer.

Thetube I is of the 55 type, that is a duplex diode-triode tube, andincludes a plurality of electrodes arrangedin the manner described inthe aforementioned Shrader application Serial No. 622,140. 7 Such a tubeincludes a pair of diode sections and a triode section which areindependent of each other. The triode section includes an 0 electronemission electrode 2, such as a unipotential cathode. This cathodepreferably comprises a sleeve extending lengthwise of the tube envelope,and contains a heater 3 which is connected to the usual alternatingcurrent heating source. The control grid 4 of the triode section isdisposed between the cathode 2 andthe main anode 5, and in actualconstruction these three electrodes are co-axial cylinders. The cathodesleeve is longerthan the triode assembly; it projects beyond the gridand main anode, and this projecting portion of the cathode sleeve is thecathode of the rectifier or double diode. This has been diagrammaticallyrepresented in Fig. 1. V

Thus, the diode anode D1'is disposed adjacent one portion of the cathodesurface, and the other diode anode D2 is disposed adjacent anotherportion ofthe cathode surface. .Both of thesecathode portionsareindependent of the cathode surface whichfurnishes the electron streamwhich flows through the grid 4150 the main anode 5. The tube I may besaid to embody a cathode which is common to both the triode and the. twodiode anodes, but the diode anodes are positioned outside'the electron.stream to .the triode grid and anode. In actual construction, the diodeanodes D1 and D2 are disposed adjacent the aforementionedprojecting endof the cathode sleeve, and

' are electrically independent of each other-and of the triode section.

These rectifier anodes may be very much smallerfthan: .those of therectifying tubes generally used in receiving sets, since :very smallcurrents 'Shrader disclosure is considered a portion of the developsufiicient rectified voltage to give the de-. siredresults; Theaforegoing description of the tube l. is believed suificient for thepurposes of the present application-inasmuch as, as statedfheretofore,the above Shrader application Serial No. 622,140 describes the said tubein great detail, and it is to be clearly understood that this saidpresent. disclosure. I

The signal voltage E0, which signal voltage in Fig. 1 isthe amplifiedoutput of. the intermediate frequencyamplifier, is shown supplied fromthe.

carrieryoltageEc is applied to thestransformer M1. 1. i Q UR.adiofrequency components are by-passed by the condenser C1, while thefilter R2*C2 permits the passage of-the direct. current voltageto thepath designatedA. :V. C. (meaning automatic volume control) without asubstantial amount of. was frequency voltage. The audio frequencycomponent developed across the resistor R1 is supplied to thegrid 4 ofthe triode section of" tube l, in proportion" to the voltage E0 and toits degree of modulation] This audio frequency component is amplified,and repeated 1-11 the cathode-anode circuit of the triode section oftube l-. Theamplified audio frequency component flowing through theresistance in the circuit of anode 5, which resistor R is in series withthe +3 terminal of .the anode potential sourcejproducesfa:voltage dropacross the resistor R which is supplied to the audio frequency amplifierof the receiver.

The grid 4 is connected to-the negative side of the resistor R1, andthis connection is made through a lead 1 thereto. Preferably, the lead Iis terminated by an adjustable tap8. The tap functions as a manualvolume control to vary the intensity of audio frequency componentdelivered Rectification. for detector .and automatic volume controlpurposes occurs between the diode plates and the cathode under theinfluenceof a signal modulated alternating voltage. The rectifiedcurrent flowing through the resistor RiJnot only produces the audiofrequency signal for the receiver, but further furnishes the automatic.

volume control bias which is supplied tothe radio 1 frequency amplifierthe firstdetector and intermediate frequency amplifier stages throughthe network including the filterR2-0z and the lead 9. It is notnecessaryto describe the. manner in which the negative bias suppliedthrough the automatic volume control network is utilized for;automatically. controlling the gain'of each of 9 the controlled stages,it beingbelieved well known to those skilledin the art how this isiaccomplished.

It is only necessary to point out that thisiis usually arranged so thatthesignal intensity leveldelivered to the transformer M1 is'maintainedsubstantially uniformras long as signal is being received. r r

. .In Fig. 2 the signal voltage E0 is applied directlyonly to the diodeplate D1 withthe result that the signal is rectified, and applied, as inFig. 1, tothe grid of the triode section by means of. coupling condenserC3. A desired amount of fixed bias may be applied to the triode gridbymeans of the source of negative; potential E3. Thediode anode D1 iseectrostatically, coupled to the diode anode D2 by means of condenser C2whereby the incoming signal is additionally supplied to the second diodecircuit. This signal, when rectified, flows. through the resistor R z,and produces a negative voltage at the righthand'end thereof; thenegative side of theresistorR'a being connected by a lead 9 to theautomatic volume con- By. biasing the anodeDi negatively with respectvto the cathode, the bias source being indicated conventionally as E1,there is no rectification of the signal until it attains a desiredpredetermined. threshold value. p This eliminates most of. the ordinarynoises present in the receiver which are not desired to be reproduced inthe absence of a signal carrier. The source ofpotential E2; is soarranged as to bias the plate D2 negatively-by a predetermined, amount;this amount necessitat ing a, peak value of signal Eo. greater than thevalue of the bias furnished'by source E2 before volume control voltageaction. can start. This produces delayed automatic volume controlaction. I 9

It will, therefore, be seen that in Fig. 2 there is shown a method orusing .two rectifier anode plates separately, one being; employed forde--v modulation andthe otherfor automatic volume; control. The signalis supplied directlytoflthe. plate D1. 7 Duringthe positive halfcyclerectified current flows through'the resistor R; by virtue ofrectification. A voltage drop occurs across the resistor R1, the latterbeing by-passed by condenser C1 to afford a low impedance path for theradio or intermediate frequencies. The audio component of rectifiedvoltage across resistor R1 is'impressed on the control grid of tube Ithrough the coupling condenser C3.

If desired, the direct connection shown in Fig. 1 may be utilized. Bybiasing the plate D1 negatively with respect to the cathode, the more orless constant tube and circuit noise voltage may be eliminated orreduced. The bias value of source E1 may be such that it is just abovethe noise level on the demodulator plate D1- This, then, serves as anoise suppressor device which functions to render the receiverdemodulator inoperative until a predetermined ratio of signal to noisevoltage is exceeded.

The capacitor C2 is of such a magnitude that it passes to the rectifieranode D2 the signal on plate D1 with but little attenuation. The sectionincluding plate D2 thus becomes an independent rectifier so far asdirect current is concerned. The resistor R2, being the externalresistor for this rectifier, has current flowing through it when theplate D2 is positive, This direct current component of rectified voltageacross resistor R2 is employed for automatic volume control.Thegeneration of automatic volume control voltage may be delayed to anydesired extent by application of the negative voltage from source E2 tothe plate D2. In this event the peak value of signal must exceed thenegative bias on plate D2 before any volume control action can beinitiated.

The source E2, therefore, represents a device for securing delayedautomatic volume control, and is' a device which functions independentlyof the noise suppressor device which governs the point at whichdemodulation can commence. Instead of a resistor B being disposed in thecircuit of the main anode of tube I, there is shown an auto-transformerL, the drop across which is employed for audio frequency amplification.

Of course, this auto-transformer may also be the primary of atransformer of the well known type.

Another modification of the invention is shown in Fig. 3 wherein thesignal transmitted through the transformer M1, this signal either beingat radio or intermediate frequency, is amplified prior to rectification,which is contrary to the procedure disclosed in Figs. 1 and 2. The'highfrequency voltage, amplified by the triode section of tube I, isimpressed on the rectifier anodes D1 and D2 by means of the capacitorCfi, which capacitor is connected between the main anode 5 and the diodeanodes D1 and D2. The capacitor U1 is of such a size that while itsimpedance to the high frequency currents is low, it has a relativelyhigh impedance to audio frequencies. Of course, in place of U1 there canbe used any other type coupling as an rj. or if. transformer. A form ofshunt feed for the triode plate 5 is used, the radio frequency choke L1preventing loss of high frequency voltage, and, at the same time,permitting direct current voltage to be supplied to the plate.

The amplified radio frequency or intermediate frequency voltage isimpressed on plates D1 and D2 together, or separately in caseindependent use of each is desired; this causes rectification to occur.The .resulting potential drop across resistor R'1 is used, in the caseof the direct componentof rectified voltage, for automatic volumecontrol through a suitable filter, and in the case of audio component ofthe rectie fied voltage, the potential drop across .resistor R1 may beused for further voltage amplification, or for power amplification. Theautomatic volume control voltage may be taken from the point indicated,that is at the negative end of the resistor R1, and the audio voltage E1may be taken from across the resistor Ri or any desired part thereof.

It will, therefore, be seen that the circuits of tube l in Fig. 3 are soarranged that the incoming signal is applied directly between thecathode and grid of the triode section, the source E4 furnishingnegative grid bias for the grid of tube I when this is desired. Theamplified voltage from the main plate circuit is delivered through thecondenser C1 to the diode plates D1 and D2 in parallel, the directcurrent flowing through the resistor R'1 under the influence of thesignal voltage producing a difference of potential. The direct currentcomponent of the potential drop across R'1 is led ofi to the automaticvolume control circuit, as employed above, and the audio component maybe taken off across the resistor R'1 in the usual manner.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

l. The combination with an electron discharge tube comprising anenvelope enclosing an electron discharge section including at least acathode, grid and plate, and a rectifier having two independent anodes,of an oscillatory circuit having one side thereof connected for radiofrequencies to both said anodes, and its other side connected to saidcathode, a resistor disposed in said other side, a connection betweenthe grid of said tube and a point of said resistor, a fixed bias sourceconnected between said grid and said cathode, an automatic volumecontrol path connected to one of said anodes, and a volume control biasresistor connected between said path and said cathode.

2. The combination with an electron discharge tube comprising anenvelope enclosing an electron discharge section including at least acathode, grid and plate, and a rectifier having two independent anodes,of an oscillatory circuit having one side thereof connected for radiofrequencies to both said anodes, and its other side connected to saidcathode, a resistor disposed in said other side, a connection betweenthe grid of said tube and a point of said resistor, a fixed bias sourceconnected between said grid and said cathode, an automaticvolume-control path connected to one of said anodes, a volume controlbias resistor connected between said path and said cathode, and meansconnected to theother of said anodes for preventing demodulationwhenever little or no signal carrier is impressed on said oscillatorycircuit.

3. The combination with an electron discharge tube comprising anenvelope enclosingan electron discharge section including at least acathode;

grid and plate, and a rectifier having two indeside, a connectionbetweenthe grid .of said .tube if latory circuit attains a predeterminedthreshold value.

4: The combination with an electron discharge tube comprising anenvelope enclosing an electron discharge section including at least acathode, grid-and plate, and a rectifier having twoindependent anodes,01 an oscillatory circuit having one side thereof connected for radiofrequenciesto both said anodes, and its other side connected to saidcathode, a resistor disposed in saidother side, a connection between thegrid of said tube anda point of said resistor, a fixed bias sourceconnected between saidgrid and said cathode, an automatic volume controlpath connected to one of said'anodes, a volume control bias resistorconnected'between said path and said cathode,

meansconnected to the other of said anodes for preventing demodulationwhenever little or'no signal carrier is impressed on said oscillatorycircuit, and means'connected to'said'volume control path and anode fordelaying the automatic volume control action until the signal carrierimpressed on said oscillatory circuit attains a predetermined thresholdvalue. V a t In combination with a'source of signal modulated radiofrequencyo carrier energy, a multiple function tube including a cathode,a signal grid, main anode and a diode anode, a signal input circuitcoupling said source to saiddiode anode and cathode, an impedance insaid input circuit across which the said carrier energy develops anaudio frequency potential, a connection from said grid to saidimpedance, an audio frequency networkcoupled to said main anode, signallevel controlmeans independent of the circuit including saidimpedanceresponsive to signals impressed on said input circuit, forproducing solely a direct current potential varying in magnitude withsig- I nal amplitude, and'means connected to said input circuit formaintaining the diode anode negative 'with. respect to the cathode untilthe impressed 50;

carrierenergy increases above aipredetermined intensity level.

6, In combination with a source of signal modulated radioofrequencycarrier energy, a multiple function tube including a cathode, a signalgrid, main anode and a diode anode, a signal input circuit coupling saidsource to said diode anode and cathode, a diode rectifier networkcoupled to said input circuit, said network including an impedance, andan automatic gain control-connection connected to a point'on saidimpedance,

an impedance in said input circuit across which the said carrier energydevelops an audio frequency potential, a connection from said grid tosaid last impedance, an audio frequency network tol'said input circuitfor maintaining the diode anode negative with respect to the cathodeuntil the impressed carrier energy predetermined intensity level.

7;;In a radio receiver, a multiple duty tube provided with at least acathode, a signal grid, a main anode,"and two diode anodes, a signalinput circuit connected between one of the diode anodes and saidcathode, said other diode anode being connected to said input circuit, aresistor in said increases above' a inputcircuit, a second'resistorconnected between V the cathode and the said other diode anode, a directcurrent connection to a point of negative potential-'on-said secondresistor, a connection between said grid and a point on "saidfirstresistor, a load circuit; connected to said main anode, and :means forbiasing said diode anodes V negatively with respect to said cathode, 7

8. In a radio receiver, a multiple duty'tube provided with at least acathode, a signal grid, a' main anode, and two diode anodes, a signalinput circuit connected between one of the diode anodes and saidcathode, said other diode anode being connectedto said input circuit, aresistor in said input circuit, a secondresistor connected between thecathode and the said other diode anoda a direct current connection to apoint" of negative potential on said second resistor, a connectionbetween said grid'and a pointon said first reanodes and said cathode,said other diode anode n V being connected to'saidinput circuit, aresistor in said input circuit, a second resistor connected between thecathode and the said other diode anode, a direct point of negativepotential on said second resistor, a connection betweensaid grid and apoint on said first resistor; a load circuit connected to said mainanode, means for biasing the'gridi'negatively with respect tosaid'cathode, and means for biasing said diode anodes negatively withrespect to saidcathode. v I

10. In a radio receiver, a multiple duty tube provided withat least acathode, a signal grid, a main anode, andtwo diode anodes, said diodeanodes being outside the electron stream to said grid and main anode, asignal input circuit conF I nected between one of the diode anodes andsaid current connection to a circuit connected to said main anode, andmeans 7 for biasing saiddiode anodes negatively with respect to saidcathode;

11. In combination with an electron discharge tube of a type includingat least a cathode and two anodes and said cathode providing independentelectron streams to said anodes, a source of modulated" radiofrequeneycarrier energy, can input circuit, tuned to the carrier frequency, con-fnected between said cathode andone of the anodes, an impedance in saidcircuit with said input circuit whereby a signal detector network isprovided a second impedance in circuit with said cathode and the secondanode and providing a carrierenergy rectifier network, an automatic gaincontrol connection to a point'on said second impedance, meansoperatively associated with the detector network for preventingdetection until a predetermined'carrier amplitude is attained; and meansoperatively associated with the recti'- fier network for delaying thegain control action amplitude is attained.

until a desired carrier DON G. BURN SIDE'.

